Only a few elements are widely used commercially in their pure form. Generally, other elements are present to produce greater strength, to improve corrosion resistance, or simply as impurities left over from the refining process. The addition of other elements into a metal is called alloying and the resulting metal is called an alloy. Even if the added elements are nonmetals, alloys may still have metallic properties.

Copper alloys were produced very early in our history. Bronze, an alloy of copper and tin, was the first alloy known. It was easy to produce by simply adding tin to molten copper. Tools and weapons made of this alloy were stronger than pure copper ones. The typical alloying elements in some common metals are presented in the table below.